1. Field of the Invention
This invention relates to an optical path switching mechanism to be used for an optical communication and an optical information processing system, and more particularly to a non-mechanical type optical path switching mechanism utilizing an electro-optic effect.
2. Description of the Related Art
Vigorous investigation and study have been made in various communication and information processing systems utilizing optical fibers. The optical path switching mechanism is indispensable art for constituting these systems.
Most of the optical path switching mechanisms now in use are of 1.times.2 type (one input by two outputs), or 2.times.2 (two inputs by two outputs.
Furthermore, in order to highly develop and diversify the optical fiber communication and information processing systems, there is a large demand for the provision of an optical path switching mechanism of m.times.n type, n.times.n type, 1.times.n type or the like having a large number of input and output terminals.
Heretofore, the above-mentioned m.times.n type or 1.times.n type optical path switching mechanism uses the above-mentioned 1.times.2 type or 2.times.2 type optical path switching mechanism as a basic component unit, and a plural number of these component units are combined into a multi-stage form or a stratified form.
For example, an optical path switching mechanism of 1.times.8 type constituted by combining 7 pieces of 1.times.2 type unit optical path switching mechanism S is shown in FIG. 9 by way of a flow chart (detailed mechanism of each of the unit optical path switching mechanisms is omitted), wherein an optical signal inputted from an input terminal is optionally taken off from any of output terminals O1 through O8 having Nos. 1 through 8. In this switching mechanism, the optical signal is unavoidably required to pass 3 pieces of the optical path switching mechanism from the time when it is inputted until the time when it is outputted. Insertion loss thereof is more than three times of that when it is required to pass only 1 piece of the optical path switching mechanism. Generally, in a 1.times.2.sup.n type optical path switching mechanism adopting the afore-mentioned system, ##EQU1## pieces of a 1.times.2 type unit optical path switching mechanism are required. In this case, the insertion loss is n times as much as that of a 1.times.2 type of unit optical path switching mechanism.
Furthermore, for example, an optical path switching mechanism of an 8.times.8 type employing a 2.times.2 type optical path switching mechanism S as its component unit and constituted by combining 32 pieces of such a 2.times.2 type unit optical path switching mechanism S is shown in FIG. 10 by way of a flow chart. In this mechanism, 8 kinds of optical signals inputted in the input terminals I1 through I8 of Nos. 1 through 8 can be optionally taken off from any of the output terminals O1 through O8 of Nos. 1 through 8. However, in this mechanism, the optical signals are required to pass 8 pieces of the unit optical path switching mechanism from the input to the output and the insertion loss thereof is 8 times as much as that when the signals pass only one unit of an optical path switching mechanism.
Generally, in the n.times.n type of optical path switching mechanism according to the above-mentioned system, 1/2n.sup.2 pieces of unit optical path switching mechanism are required. In this case, the insertion loss is n times as much as that of the unit optical path switching mechanism.
Furthermore, when an optical path switching mechanism is constituted by using the 1.times.2 type unit optical path switching mechanism shown in FIG. 9 as a basic component unit, the insertion loss thereof exceeds the allowable range extensively.
Accordingly, the characteristic requirements of a 1.times.n type, n.times.n type or m.times.n optical path switching mechanism are that, first, the insertion loss is small, second, it can be made small in bulk, third, switching speed is fast, and fourth, crosstalk characteristic is high.
Furthermore, the optical path switching mechanisms presently contemplated are largely classified into two types; one is a non-mechanical type optical path switching mechanism utilizing an electro-optic effect or magneto-optic effect, and the other is a mechanical type optical path switching mechanism wherein the optical path is switched by mechanically actuating an optical element such as a prism, etc. The former is further classified into two types, one is a photo-conductive wave path type switch chiefly used for a single mode fiber and the other is a bulk type optical path switch chiefly used for a multi-mode fiber. Although both facilitate a high switching speed, they present shortcomings or drawbacks in that if they are combined in multi-stages to constitute an optical path switch mechanism, the insertion loss becomes too large.
On the other hand, the latter mechanical type optical path switch mechanism renders a low insertion loss characteristic as well as a superior crosstalk characteristic, and therefore seems to be suitable for the optical path switch mechanism of m.times.n type, 1.times.n type, etc. However, since it is driven mechanically, it presents vital shortcomings in that the switching speed is extremely slow and a driving apparatus thereof becomes too bulky. Because of the foregoing reasons, such a switch mechanism is not actually employed in an optical path switch mechanism having a large number of input and output terminals.
The present invention was accomplished in order to overcome the above-mentioned shortcomings or drawbacks of the prior art.